AAT3142ITP-T1 AnalogicTech, AAT3142ITP-T1 Datasheet - Page 11

• Manufacturer Part Number: AAT3142ITP-T1
• Description: High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
• Manufacturer: AnalogicTech

S
The current source output magnitude is controlled by the
EN/SET pin, using AnalogicTech’s S
interface records rising edges of the EN/SET pin and
decodes them into 32 individual current level settings
with Code 1 reserved for no current. Once EN/SET has
been held in the logic high state for time T
grammed current is seen at the current source outputs,
and the internal data register is reset to 0. For subse-
quent current level programming, the number of rising
edges corresponding to the desired code must be
entered on the EN/SET pin.
When EN/SET is held low for an amount of time greater
than T
draws less than 1μA from V
is reset to 0 during shutdown.
LED Selection
The AAT3142 is specifically intended for driving white
LEDs. However, the device design will allow the AAT3142
to drive most types of LEDs with forward voltage speci-
fications ranging from 1.0V to 4.3V. LED applications
may include main and sub-LCD display backlighting,
camera photo-flash applications, color (RGB) LEDs,
infrared (IR) diodes for remotes, and other loads benefit-
ing from a controlled output-current generated from a
varying input-voltage. Since the D1 to D3 output current
sources are matched with negligible voltage dependence,
the LED brightness will be matched regardless of the
specific LED forward voltage (V
In some instances (e.g., in high luminous output applica-
tions such as photo flash), it may be necessary to drive
high-V
the AAT3142 make it capable of driving LEDs with for-
ward voltages as high as 4.3V at full current from an
input supply as low as 3.0V. Outputs can be paralleled to
drive high-current LEDs without complication.
S
ChargePump
3142.2009.07.1.3
2
2
Cwire Serial Interface
Cwire Serial Interface Timing
OFF
F
type LEDs. The low-dropout current sources in
, the AAT3142 enters into shutdown mode and
TM
High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
Data Reg
EN/SET
IN
. The internal data register
F
) levels.
2
Cwire interface. The
1
2
LAT
, the pro-
w w w . a n a l o g i c t e c h . c o m
T
LO
n-1
0
T
HI
n <= 32
T
LAT
Termination of Unused
Current Source Outputs
If any outputs (D1 to D3) are not used, they should be
terminated by connecting the respective unused output
directly to ground. This is required to assure correct
charge pump mode operation. If a given unused output
is not terminated to ground, it will appear to the respec-
tive output’s feedback control as an infinite impedance
load and the unused constant current source will be set
for a maximum voltage. Although no current flows from
the unused current source, the voltage sensed at that
node could force the charge pump control to activate the
charge pump when it is not necessary. To prevent this
effect, simply connect the unused constant current
source outputs to ground.
Device Switching Noise Performance
The AAT3142 operates at a fixed frequency of approxi-
mately 1MHz to control noise and limit harmonics that
can interfere with the RF operation of cellular telephone
handsets or other communication devices. Back-injected
noise appearing on the input pin of the charge pump is
20mV peak-to-peak, typically ten times less than induc-
tor-based DC/DC boost converter white LED backlight
solutions. The AAT3142 soft-start feature prevents noise
transient effects associated with inrush currents during
start-up of the charge pump circuit.
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following
sections only accounts for efficiency of the charge pump
section itself. Due to the unique circuit architecture and
design of the AAT3142, it is very difficult to measure
efficiency in terms of a percent value comparing input
power over output power.
n
T
OFF
PRODUCT DATASHEET
0
AAT3142
11